The invention relates to methods and apparatus for testing the wrappers of cigarettes, cigars, cigarillos, cigarette filters, other rod-shaped smokers' articles, and the like.
More specifically, the invention relates to methods and apparatus for such purpose of the type in which there are generated a first signal indicative of the air permeability of the wrapper of the article, a second signal indicative of the porosity of the material of the wrappers of the articles, and a third signal derived from the first and second signals and indicative of that component of the air permeability of the wrapper of the article not attributable to the porosity of the wrapper material itself.
In the cigarette-manufacturing industry, it is known to test the wrappers of cigarettes, cigars, cigarillos, cigarette filters, filter cigarettes, other rod-shaped smokers' articles, and the like. The testing of the wrappers is intended to detect the presence of holes in the wrapper paper, imperfectly formed seams in the wrapper, defective joints between the tobacco-containing section of a filter cigarette and the filter head thereof, and other defects which could detrimentally affect the smoking experience by causing a significant inflow of adjoining air through the defective wrapper when the smoker inhales through the cigarette, or the like.
For example, it is known to assess the integrity of a cigarette wrapper by sealing off one end of the cigarette and by known means connecting the other end of the cigarette to a source of pressurized air. If there are breaks or seam defects in the wrapper, then a sizable airflow outwards through the wrapper defects will occur. This outwards airflow can be detected by monitoring the air pressure of the air entering the cigarette. For example, if there is a sizable opening in the wrapper seam, permitting a sizable airflow out through this opening, the air pressure upstream of the cigarette will be lowered; conversely, if the integrity of the wrapper is complete, there will be comparatively little airflow out through the wrapper and this can be detected in the form of a comparatively high pressure upstream of the cigarette.
However, an ever-present problem with this and other such wrapper testing methods is constituted by the porosity of the material of the wrapper. Because the material of the wrapper may be quite porous, a considerable amount of air may flow outwards through the surface of the material of the wrapper, for example when performing a wrapper test of the type just described. That component of the total air permeability of the wrapper specifically attributable to the porosity of the wrapper material itself in general cannot be distinguished from the component attributable to wrapper defects, and accordingly the generation of a signal indicative of the total air permeability of the wrapper is of only limited usefulness. For example, the total air permeability of a high-porosity wrapper having no defects may be greater than the total air permability of a comparatively low-porosity wrapper having completely unacceptable defects; as a result, it is to an unsatisfactory extent necessary either to discard acceptable articles or not to discard unacceptable articles.
The porosity of the material of the wrappers changes markedly, in particular, from one supply reel to the next. Accordingly, when changing wrapper material supply reels, a large number of articles may be automatically rejected by the testing apparatus before the operating personnel can effect the necessary readjustments and corrections. The loss of so many articles which may in fact be perfectly acceptable is of course undesirable, and the necessity of repeatedly readjusting the testing apparatus is very inconvenient.
West German Published Patent Application No. 2,109,412 discloses an arrangement for automatically adjusting the wrapper testing apparatus in response to fluctuations in the porosity of the material of the wrappers. The porosity of the wrapper material is determined separately from the determination of the total air permeability of the wrapper of the finished article. Specifically, the wrapper material, prior to the actual manufacture of the finished article, is conducted past a suction chamber. The suction in the suction chamber is a direct indication of the porosity of the wrapper material. The suction in the suction chamber is detected and converted into a corresponding control signal. The control signal is then employed to automatically compensate for the porosity of the wrapper material, by automatically adjusting the pressure of the air used to test the wrappers of the finished articles made from the measured wrapping material. This known arrangement is of dubious operability for various practical reasons. It is very difficult to establish a complete enough seal between the wrapper material and the interior of the suction chamber. Additionally, which cannot be seen very clearly from the drawing of the publication in question, the two testing arrangements are located quite far from each other in space. The one is located at the input of the cigarette rod machine whereas the other is located at the output of the filter attachment machine; as a result, before a finished article made from the wrapper material whose porosity has been measured actually reaches the wrapper testing station, fifty to sixty articles may have already passed the wrapper testing station. Accordingly, although an automatic correction is supposedly achieved, it is at best achieved with a very considerable time delay. Moreover, if the wrapper material itself is defective over a considerable length, for example if it is replete with sizable holes and tears, this will be misinterpreted as a more increase of the porosity of the wrapper material, and the pressure of the air used at the wrapper testing station will be correspondingly adjusted. As a result, at the wrapper testing station, the defective finished articles made from the defective wrapper material section will not be detected as being defective.
We have considered the possibility of detecting wrapper material porosity fluctuations using the testing apparatus for the wrappers of the finished articles and, in correspondence to such detection, correcting the results of the wrapper tests. The pressure of the test air used for testing the wrappers of the finished articles would be applied to a pneumatic storage connected to one input of a differential pressure meter to whose other input is applied the test pressure. The pressure in the storage would adjust itself to long-term or persisting changes in the test pressure, whereas short-lasting changes would be registered by the differential pressure meter. A disadvantage of this approach is that, upon start-up of the testing apparatus, the pressure in the pneumatic storage must first build up to an operational value, and this results in the rejection of the first forty to fifty articles. Furthermore, in the event that a series of articles are all defective, the pressure in the pneumatic storage will gradually adjust itself to the pressure associated with the defective articles, with the result that subsequent defective articles will not be detected as being defective.